class Solution {

    public String frequencySort(String s) {

        Map<Character,Integer> map = new HashMap<>();

        //放入map

        for(char c :s.toCharArray()){

            if(map.containsKey(c)){

                map.put(c,map.get(c)+1);

            }else

                map.put(c,1);

        }

        //根据value的大小排序

        Comparator<Map.Entry<Character,Integer>> comparator =

            new Comparator<Map.Entry<Character, Integer>>() {

             @Override

             public int compare(Map.Entry<Character, Integer> o1, Map.Entry<Character, Integer> o2) {

                 return o2.getValue() - o1.getValue();

             }

         };

        //放入链表

        List<Map.Entry<Character,Integer>> list = new ArrayList<>(map.entrySet());

        //根据实现的comp排序

        Collections.sort(list,comparator);

        //定义数组

        StringBuilder sb = new StringBuilder();

        for(Map.Entry<Character,Integer> entry : list){

            for(int i = 0 ; i < entry.getValue();i++){

                sb.append(entry.getKey());

            }

        }

        return sb.toString();

    }

}